We present 3-D analytical models for subthreshold swing, threshold voltage and threshold volatge roll-off of undoped FinFET devices. After solving the 3-D Poisson equation, in which the mobile charge term was included, we have obtained an expression of the electrostatic potential through the device. We have validated the threshold voltage, subthreshold swing, and threshold voltage roll-off models by comparison with 3-D numerical simulations and measured values; a good agreement with both 3-D numerical simulation and the experimental results has been observed.